Optimal criteria for detecting bolus passage across the pharyngo-oesophageal segment during the normal swallow using intraluminal impedance recording

The impedance criteria for the detection of the arrival of bolus head and clearance of bolus tail in the pharynx have not been defined, and may differ from accepted criteria used in the oesophagus. Our aim was to define the optimal impedance criteria that most accurately defined passage of the swallowed bolus moving through the pharyngo-oesophageal segment. In eight healthy volunteers, an assembly incorporating seven impedance-measuring segments was positioned across the pharyngo-oesophageal segment, and subjects swallowed liquid and semisolid radio-opaque boluses (2-20 mL) while impedance was simultaneously recorded with videofluoroscopic images. To derive the optimal criteria, in an iterative process we correlated impedance defined bolus presence with fluoroscopy (Cohen's Kappa) for a range of impedance cut-off values from 100% to 0% for both the initial fall, and recovery of impedance. Bolus presence in the pharynx, as determined by the 'standard' criteria (50% drop and recovery to 50% of baseline), correlated very modestly with videofluoroscopy (kappa approximate to 0.35). The criteria that most accurately defined bolus passage varied between pharyngeal regions. Threshold (% of baseline) for bolus head entry into the region ranged from 71% to 80%. Threshold for bolus tail clearance varied from nadir to 19%. Correlation of impedance with videofluoroscopy improved to kappa approximate to 0.6 with the above criteria. The impedance criteria defining bolus presence across the pharyngo-oesophageal segment differ from those adopted in the oesophagus. Pharyngeal impedance provides an accurate, non-radiological indicator of bolus transit through the pharynx.